Cook the manicotti shells according to package directions until al dente.
Drain, rinse with cold water to stop the cooking process, and drain again.
Set aside.
While the pasta cooks, preheat your oven to 350°F / 175°C.
Coat a medium skillet with nonstick cooking spray and heat over medium heat.
Add the chopped mushrooms and green onions, cooking and stirring occasionally until tender.
Stir the crushed Italian seasoning into the mushroom mixture and cook for another 30 seconds until fragrant.
Remove the skillet from the heat.
In a medium bowl, thoroughly mash the drained tofu with a potato masher or fork until it resembles the texture of ricotta cheese.
Stir in the cooked mushroom mixture, the lightly beaten egg, and the Parmesan cheese until well combined.
Carefully fill each cooked manicotti shell with about 1/4 cup (960 ml) of the tofu filling.
Arrange the filled shells in a single layer in an ungreased 3-quart rectangular baking dish or four individual 12- to 15-ounce au gratin dishes.
In another medium bowl, combine the undrained diced tomatoes, condensed tomato bisque, and black pepper.
Pour this sauce evenly over the filled manicotti shells, ensuring they are well-covered.
Bake, uncovered, for about 30 minutes, or until the sauce is bubbly and the filling is heated through.
Sprinkle the shredded Italian cheese blend over the top.
Return the dish to the oven and bake for 2 to 3 more minutes, just until the cheese is perfectly melted and gooey.
Let the manicotti stand for 10 minutes before serving to allow it to set.
Boil pasta until just al dente before adding it to the casserole. It will continue to cook in the oven, and this prevents it from becoming mushy.
